It is desirable, in the textile arts, to impart especially to synthetic yarns, i.e. monofilamentis or multifilaments! which may be spun from a synthetic resin through a spinneret, various textures or "effects" to improve the "hand" or appearance of fabric which is made from such yarn filaments.
It has been proposed, for example, to form synthetic filament yarns or, more generally, synthetic filaments, with alternating thick and thin regions. However, such yarns tend to be incompletely stretched over sections of the length of the filament and, since stretch improves the molecular orientation and hence the crystallinity of the filament, in some cases, the thick/thin filaments which resulted had insufficient strength in the regions of less stretch and were more sensitive to deterioration the presence of light in such regions. The elongation properties also were reduced in the regions of less stretch.
In practice, incompletely stretched filaments were not usable for curtains and the like which had to be subjected to relatively intense light over many years because the filament strength would deteriorate to say a third of the original strength and the elongation to break could be reduced from 30% to 5%, representing a major deterioration of quality. The production of variations in the thickness of a filament is described, inter alia in the publication for "Verfahren zum Erzeugen von periodischen Feinheitschwankungen an fadenformigem Gut" by Tatjana Sinjunkowa, KDT, Technische Universitat Karl-Marx-Stadt, Sektion Textil- und Ledertechnik, Textiltechnik Volume 39 (1989), No. 5, pg. 229 ff.